1. Field of the Invention
The present invention is related with an optical disk, an optical disk reproducing apparatus, and an optical disk recording apparatus, and more specifically, it is related with the optical disk and the optical disk reproducing apparatus, in which a high density record is possible.
2. Description of the Related Art
FIG. 1 shows a constitution of an information recording surface of a magneto-optical disk.
In the magneto-optical disk, grooves G, which are approximately coaxially arranged guiding grooves, are formed, and lands L are formed along with the grooves G. Information pits (record marks) are normally formed on the lands L. In order to read out the information pit without error, the groove G is kept in such a state that nothing is recorded thereon.
If the information pit is formed on both of the land L and the groove G with respect to the magneto-optical disk, a crosstalk is generated so that there arises a problem that the information pit cannot be correctly read.
In order to solve the above-mentioned problem, there is a super resolution reproduction, such as a MSR (Magnetically induced Super Resolution).
The super resolution is such a technology, which is developed in the field of a microscope, that a high resolution exceeding a usual definition is obtained by a special process applied to the image formation system, or by the post process applied to the image. For example, there is one method of dividing a spacial frequency domain into some pieces, performing the image formation in each domain, and synthesizing them on the image formation plane. There is another method of performing an image formation after modulating the object image by use of a lattice, and demodulating it on the image formation plane.
Hereinbelow, the MSR as one technique of the super resolution reproduction, will be explained. In the technical field of the microscope, it is known that the image resolution can be improved by preparing an optical mask like a pinhole at an objective position. In the MSR, a physical mask is not prepared at the recording medium surface of the magneto-optical disk, but a mask is formed in efficiency in the medium by use of the temperature distribution in the medium. The MSR enlarges the spacial frequency of the reproduction limit in efficiency, whereby to improve the recording density to about 1.5 to 3 times (see in detail "Atsushi Fukomoto, super resolution in a magneto optical disk with an active mask" in Japanese Applied Magnetic Academy's paper, Vol.15, No.5.1991, etc.).
However, in the above-mentioned MSR, in order to perform the super resolution reproduction, it becomes necessary to magnetically record the information pit, or the address pit for address generation.
Therefore, with respect to the optical disk, on which the address pit is recorded in advance as a phase pit in the same manner as the information pit of a ROM disk etc., the above-mentioned super resolution reproduction cannot be applied to the reproduction of the address pit. Thus, the address pit needs to be formed in such a large size that allows a normal reproduction (normal resolution reproduction). Even if the information pits are formed on both of the land L and the groove G in order to improve the recording density, it is not possible to make the address pit correspond to both of the land L and the groove G by one to one, resulting in a problem that a perfect information reproduction cannot be performed.